A flow rectifier of the above described kind is an air directing element, which is disposed with the air guide blades thereof directly behind an axial fan in order to redirect the air that has been set in motion by the impeller of the axial fan in a flow that is as axial and as uniform as possible. An air directing element of this kind is frequently also referred to as a “streamer”.
Axial fans are used, among other things, in evaporators in cold storage rooms, where the cold air is distributed by an axial fan via a heat exchanger into the cold storage room. In the case of large cold storage rooms, it is important that the cold air be transported as far as possible into the room in order that refrigerated products located at a great distance can also be cooled. To this end, an axial fan is needed that provides the greatest possible volumetric flow with a large trajectory distance. Here, a trajectory is understood to be a distance up to which a critical velocity of the air flow is maintained. This trajectory is limited due to the swirl-impaired outflow of an axial fan. The trajectory distance can be significantly increased with the help of a downstream flow rectifier, which transforms the swirling movement back into a uniform, axial flow. It is important here that the flow rectifier have as little flow resistance as possible so that only an insignificant degree of pressure drop occurs in the quantity of air flowing therethrough.
A flow rectifier of the aforementioned type, which essentially fulfills the requirements specified above, is known from DE 44 04 262 A1. A reduction in the swirling movement of the flow medium is achieved here in particular by the fact that, viewed in the circumferential direction, the air guide blades each extend with a curvature relative to the axial direction between an inflow-side blade edge and an outflow-side blade edge. In a special embodiment, it is also provided here that one of the blade edges, and specifically the edge on the front of the guide blade, has an adjustable height in the radial direction. Said blade edge is designed such that it is straight, and extends at an angle to the central axis of the impeller. An effect possibly associated with this design is not described.
A disadvantage to this known flow rectifier is that an actually uniform, axial flow only arises at a considerable distance from the fan or from the exit out of the guide wheel. In this way, as shown in FIG. 1 contained in DE 44 04 262 A1, while an angle between the air flow and the fan axis in a peripherally located optimal region of the radial length of the air guide blades of the flow rectifier is virtually zero, this angle nevertheless increases rather quickly radially outward and, in particular, radially inward therefrom. This results in a diverging air flow. In the case of the given diameter of the cylindrical curved surface areas of the walls, which delimit the ring of the air guide blades radially inside and outside, there is only one optimum blade length from the standpoint of rendering the flow of fluid uniform, which length, according to DE 44 04 262 A1, was determined through extensive aerodynamic measurements using a Conrad sensor. In addition, when using the known flow rectifier, a combination of said rectifier with a protective grill is necessary in order to ensure protection against accidental contact.
In addition, US 2005/0186070 A1 discloses a fan assembly including an impeller, which is disposed on the rotor of a motor. The impeller is surrounded by a housing, wherein the housing comprises a flow rectifier disposed behind the impeller in the direction of flow. The blades of the flow rectifier have a consistent height in the radial direction.
The object of the present invention is to create a flow rectifier of the above-mentioned type, using which the aforementioned disadvantages can be overcome while achieving a high volumetric flow and large trajectory distance.